1. Field of the Invention
The invention relates generally to integrated circuits and more specifically to integrated circuits in which a diamond structure is bonded to the substrate of the integrated circuit.
2. Description of Related Art
Modern integrated circuits are becoming increasingly complex. Advances in lithography and other manufacturing technologies allow the size of transistors and other components to be reduced, which in turn allows more components to be placed on the chip. Typical integrated circuits may contain more than a million electronic components on a single chip.
As the complexity of integrated circuits grows, the power and cooling requirements of the integrated circuits also grow. Since there are a greater number of electrical components on the chips, each of which requires power to operate, the overall power required to drive the chips increases. Then, since the chips require more power, they dissipate more heat. This heat must be removed from the chips to prevent overheating which could damage the chips. Another problem which exists is the presence of temperature gradients in the chip. Depending upon the design and the execution of software in the chip, the power density may vary from point to point on the chip. These localized hot and cool spots and the resulting temperature gradients should be minimized to reduce the risk of damage to the chip.
Many integrated circuits use heat sinks or heat exchangers to efficiently remove excess heat. These heat exchangers typically consist of metal (e.g., aluminum) bodies which are connected to the package of the chip. It is important to ensure good thermal contact between the integrated circuit and the heat exchanger so that as much heat as possible is transferred from the integrated circuit to the heat exchanger. Heat exchangers may include fins or other structures which allow the energy absorbed by the heat exchanger to be transferred to the surrounding environment.
Metal heat exchangers are typically bonded to integrated circuit packages by soldering. The heat exchanger cannot simply be soldered directly to the package. The package must first be coated with a layer of a reactive metal (e.g., titanium) and then a layer of a solderable metal (e.g., copper.) The heat exchanger can then be soldered to the layer of solderable metal.
Not all heat exchangers are constructed of metal. Because diamond has very good thermal conductivity (better than metal, in fact,) it can also be used in a heat exchanger or heat spreader. Conventional methods of attaching diamond to integrated circuit packages are very similar to the methods used with metal heat exchangers. Referring to FIG. 1, a diagram illustrating the structure of an integrated circuit package having a diamond heat spreader is shown. In the case of diamond, instead of coating only the package 11 with layers of reactive 12 and solderable 13 metals, both package 11 and the diamond 14 are coated in this manner. The solderable metal layers are then bonded by a layer of solder 15.
Conventional methods of bonding diamond heat spreaders to integrated circuits present several problems. First, it is both expensive and time consuming to deposit the layers of metal on the substrate and heat spreader. Second, when the solderable layers are soldered together, there may be bubbles or voids 16 remaining in the solder layer. Since very little thermal energy is transmitted through these voids, the heat transfer path from the substrate to the heat spreader is restricted. This is illustrated by the arrows in FIG. 1. Further, the uneven distribution of thermal energy in the heat spreader cause temperature gradients which may damage the integrated circuit. Third, when the solder is applied, it and at least the surfaces of the solderable layers are at a temperature above the melting point of the solder. As the solder hardens and it and the other layers cool, they contract. Because they contract at different rates, stresses are built up between the layers, potentially causing delamination of the layers and damage to the integrated circuit and heat spreader.